The present invention relates to a highly heat-conductive ceramic material. More particularly, it relates to a ceramic material exhibiting excellent heat radiation, having high density and being rich in electrical insulation.
There has recently been great progress in integration of electronic equipment as seen from the development of IC, LSI, etc., and it has been strongly desired to develop insulating material having excellent heat radiation property.
As such an insulating material, various kinds of ceramics have been widely used. For instance, ceramics made of aluminum oxide (Al.sub.2 O.sub.3) are predominantly for IC substrates. Berylium oxide (BeO) is also used for such materials, and some of the materials have begun to employ silicon carbide (SiC), boron nitride (BN) and aluminum nitride (AlN).
The Al.sub.2 O.sub.3, however, has its limitation in heat-conductivity (about 30 W/m.degree. K at best) and is not suitable for enhancing its heat radiation property. In the case of BN, ceramics of hexagonal system are poor in strength and those of cubic system are as expensive as a diamond, both of which are accordingly not suitable for common use and not advantageous industrially. As to the AlN, those which are practically used contain inevitable impurities such as oxygen or a trace amount of Si, although they are highly heat-conductive theoretically. As a result, they only show the heat-conductivity about 2 to 3 times better than that of Al.sub.2 O.sub.3. Further, SiC is also a material having high heat-conductivity. However, its electrical resistance is generally poor and is not suitable for insulating materials.
Recently, there has been development of SiC-BeO system materials which have both the great insulating property and the heat conductivity, as reported in Japanese Laid-Open Patent Applications Nos. 66086/1981, 2591/1982 and 15484/1982. These materials, however, cannot be used under a high voltage since they have varistor characteristics, and in addition, are inconvenient for practical use since they require the poisonous substance Be during their production steps.
Thus, it has long been desired to provide materials having further superior heat radiation property and simultaneously having high insulating property, because the conventional highly heat-conductive ceramics have both advantages and disadvantages.